This invention relates to a tube pump using deformation of a tube for generating pressure and an ink jet recording apparatus comprising recovery device of an ink ejection capability for discharging ink from a recording head using negative pressure generated by the tube pump.
An ink jet recording apparatus produces comparatively small noise at the printing time and moreover can form small dots at a high density and thus nowadays is widely used for print centering on color print.
Such an ink jet recording apparatus comprises an ink jet recording head for receiving ink supplied from an ink cartridge and paper feed device for relatively moving record paper to the recording head.
While the recording head is moved in response to a print signal, ink droplets are ejected onto record paper for forming dots, thereby recording. In this case, a recording head capable of ejecting black ink, yellow ink, cyan ink, and magenta ink, for example, is mounted on a carriage and the ink ejection percentage is changed, thereby making full color print possible.
Since such an ink jet recording apparatus ejects ink onto record paper as ink droplets through nozzle openings for printing, it involves the following problem: clogging occurs in the nozzle openings due to a rise in ink viscosity caused by evaporation of an ink solvent from the nozzle openings, ink solidification on the nozzle formation face, or deposition of dust and further air bubbles are mixed into the recording head, causing a print failure to occur.
Thus, in addition to the recording head and the paper feed device, the ink jet recording apparatus comprises capping device for sealing the nozzle formation face of the recording head in a non-print mode, a suction pump for sucking and discharging ink into the capping device, and wiping device for cleaning the nozzle formation face of the recording head after ink is sucked and discharged by the suction pump.
To prevent clogging from occurring in the nozzle openings and air bubbles from being mixed into the recording head, ink is forcibly sucked and discharged from the recording head into the capping device by the suction pump (ink ejection capability recovery processing) and then the nozzle formation face of the recording head is wiped by the wiping device.
The forcible discharge processing of ink performed to remove clogging of the recording head or if air bubbles remain in the recording head is called cleaning operation. The cleaning operation is performed when print is restarted after the recording apparatus is in a nonoperating mode for a long time or when the user recognizes a print quality failure of faint print, etc., and presses a cleaning switch.
To perform the cleaning operation, the recording head is sealed with the capping device and a negative pressure is made to act on the inside of the capping device.
Used as a device for feeding a negative pressure into the capping device is a tube pump which has a comparatively simple structure, can be easily miniaturized, and moreover does not cause pollution in the mechanical portion for sucking and discharging ink.
The tube pump has a configuration, for example, as shown in FIGS. 7 and 8. FIG. 7 shows a pump operation state as the pump is driven in a forward direction and FIG. 8 shows a release operation state as the pump is driven in a reverse direction.
The tube pump shown in FIGS. 7 and 8 comprises a pump frame 44 having a tube support face 52 for guiding the outer shape of a flexible tube 51 to be a circular-arc manner, a pump wheel 42 rotated by a paper feed motor, for example, and rollers 43a and 43b having roller shafts 43A and 43B moving along roller support grooves 42a and 42b opened to an end face of the pump wheel 42.
The pump frame 44 is formed with L-shaped retention grooves 44a and 44b opposed to the tube support face 52 and guide members 53a and 53b made of elastic material projecting in the center direction of the pump wheel 42 are retained in the retention grooves 44a and 44b. 
In such a tube pump, if the pump wheel 42 is rotated in the normal direction (arrow A direction) as shown in FIG. 7, the rollers 43a and 43b move in the outer peripheral direction of the roller support grooves 42a and 42b and are rotated and rolled while pressing the flexible tube 51 in the arrow A direction. Accordingly, a pressure is generated in the flexible tube 51 for feeding a negative pressure into the capping device. Ink is forcibly discharged from the recording head by the negative pressure and further the ink discharged into the capping device is sucked and is sent to a waste ink tank.
If the pump wheel 42 is rotated in the reverse direction (arrow B direction) as shown in FIG. 8, the rollers 43a and 43b move in the inner peripheral direction of the roller support grooves 42a and 42b and are rotated and rolled in the arrow B direction while keeping the flexible tube 51 in the release operation state in which the rollers 43a and 43b come in contact with the flexible tube 51 only a little. Accordingly, failure occurrence of the roller 43a, 43b sticking to the flexible tube 51 or the like is prevented.
In this case, the guide members 53a and 53b act so as to guide the rollers 43a and 43b in the wheel rotation backward direction of the roller support grooves 42a and 42b as the pump wheel 42 is rotated.
However, in this kind of tube pump, when the pump operation state is switched to the release operation state, the rollers 43a and 43b rotate and roll with the pump wheel 42 while pressing the flexible tube 51, and thus the following problem is involved. That is, just after the pump operation state is switched to the release operation state, the rollers 43a and 43b receive such a force displacing in the wheel rotation direction with the rollers 43a and 43b pressed into contact with the flexible tube 51 from the groove walls of the roller support grooves 42a and 42b and thus fluids of ink, air, etc. which are sucked into the flexible tube 51 flow back and the reliability on the pump quality is degraded.
On the other hand, to use the tube pump with the ink jet recording apparatus, ink bubbles are produced in the capping device because of flowback of ink, etc. which is sucked from the recording head and some of the ink bubbles may be exposed to the outside of the capping device.
If the ink bubbles are thus exposed to the outside of the capping device, when the recording head is next sealed with the capping device, as they come in contact with each other the ink bubbles are broken and this action may cause instantaneous air pressure change to occur in the nozzle openings of the recording head, destroying meniscuses of ink formed in the nozzle openings.
Consequently, the normal ejection operation of ink droplets through the nozzle openings cannot be accomplished, causing a print fault called missing dots to occur, leading to degradation of the reliability on cleaning; this is a problem.
It is therefore an object of the invention to provide a tube pump for making it possible to enhance reliability on pump quality, simplify the whole structure, and reduce costs and an ink jet recording apparatus using the tube pump to make it possible to enhance reliability on cleaning.
To this end, according to the invention, there is provided a tube pump comprising:
a pump frame having a tube support face for guiding a curve of a flexible tube in a circular-arc manner;
a pump wheel rotatably disposed in the pump frame and having a roller support groove; and
a roller having a roller shaft, disposed rotatably and rollably on the pump wheel and relatively displaceable between a pump operation position and a release operation position in the roller support groove, the roller being configured to deform the flexible tube by a press contact so as to generate a pressure in the tube pump;
the roller shaft being guided by a groove wall in contact therewith;
wherein the groove wall of the roller support groove is provided with a cam face configured such that
the roller is relatively displaced from the release operation position to the pump operation position in a state that the roller rotates and rolls, when the pump wheel rotates from a release operation state in a pump operation direction; and
the roller is relatively displaced from the pump operation position to the release operation position in a state that the roller does not rotate and roll, when the pump wheel rotates from a pump operation state in a release operation direction.
Since the tube pump is thus configured, when the release operation state is switched to the pump operation state, the roller rotates and rolls and receives such a force displacing from the release operation position to the pump operation position from the groove wall of the roller support groove. On the other hand, when the pump operation state is switched to the release operation state, the roller remains immobile and receives such a force displacing from the pump operation position to the release operation position from the groove wall of the roller support groove.
Therefore, just after the pump operation state is switched to the release operation state, the roller is prevented from rotating and rolling in the wheel rotation direction while pressing the flexible tube, so that fluids of ink, air, etc., sucked in the flexible tube do not flow back and the reliability on the pump quality can be enhanced.
Here, it is desirable that a cam curve of the cam face should be a curve with an arbitrary point on a line represented by polar coordinates (r, xcex8) wherein the rotation center of the pump wheel is the origin, radius r is a function of angle xcex8 found from r=C1xc3x97exp (xcex1xc2x7xcex8), and end angle xcex8xcex2 is a constant found from xcex8xcex2=(1/xcex1)xc3x97log (C2/C1), that polar coordinates (r, xcex8) of both end points on the curve should be set to predetermined polar coordinates (C1, 0) and (C2, xcex8xcex2), and that pressure angle xcex1 of the cam face with respect to the roller shaft should be set to a predetermined angle in the range of xcfx80/30 less than xcex1 less than xcfx80/20.
Since the tube pump is thus configured, if the pressure angle xcex1 is xcex1=7xcfx80/180 (7xc2x0) or xcex1=8xcfx80/180 (8xc2x0), just after the pump operation state is switched to the release operation state, the roller is prevented from rotating and rolling in the wheel rotation direction while pressing the flexible tube, so that the reliability on the pump quality can be enhanced.
If xcex1=xcfx80/30 (6xc2x0), after the pump operation state is switched to the release operation state, the roller does not move toward the release operation position at an intermediate point of the roller support groove and moves interlockingly with the pump wheel while pressing the flexible tube. If xcex1=xcfx80/20 (9xc2x0), just after the release operation state is switch to the pump operation state, the roller does not move toward the pump operation position and moves interlockingly with the pump wheel.
It is desirable that a roller guide having a guide face for guiding the roller shaft is placed on the axis of the pump wheel.
Since the tube pump is thus configured, when the roller shaft moves within the roller support groove, it is guided by the roller guide.
The tube support face may be provided such that the contact area between the flexible tube and the roller is formed all around the pump wheel.
Since the tube pump is thus configured, the contact area becomes long in the circumferential direction and thus a higher negative pressure can be provided as compared with the tube support face such that the contact area between the flexible tube and the roller is provided on half of the circumference of the pump wheel.
Further, the roller support groove is a single roller support groove at a position eccentric from the rotation center of the pump wheel.
Since the tube pump is thus configured, a single roller can be placed for the pump wheel.
The configuration wherein the roller support groove is a pair of roller support grooves positioned at parts symmetrical with respect to a point about the rotation center of the pump wheel can also be adopted.
Since the tube pump is thus configured, a pair of rollers can be placed for the pump wheel.
On the other hand, according to the invention, there is provided an ink jet recording apparatus comprising an ink jet recording head for ejecting ink droplets in response to print data; and capping device for sealing the nozzle formation face of the recording head and sucking and discharging ink from the recording head upon reception of a negative pressure from a pump unit, characterized by the above-described tube pump as the pump unit.
Since the ink jet recording apparatus is thus configured, fluids of ink, air, etc., sucked from the recording head can be prevented from flowing back into the capping device.
Therefore, ink bubbles produced as in the related art are not produced, so that destroying of meniscuses as ink bubbles are broken can be prevented.
Thus, the normal ejection operation of ink droplets through the nozzle openings can be accomplished, so that a print fault called missing dots does not occur and the reliability on cleaning can be enhanced.